Your hosts file isn't correct and according to you dig output, you appear to have no MX record for your Zimbra server. You can find the information about your hosts file in the Quick Start Installation Guide (and all over the forums). You can also follow the Split DNS instructions for setting up your DNS records.

According to your forum profile you have Zimbra 4.5.3, is that correct? If it's not correct then please update it with the version you currently have (or are trying) installed.

BTW, when you do a dig command you use the domain name not the FQDN of the server. So you should use:

Thanks your advise. But I still confuse that must I set up split DNS? Because this mail server was OK till yesterday it was down. I modify the hosts file to add mydomain.com and IP address, but it still can not work. How to fix it? What should I do? I appreciate your help. Thank you!
BTW, this mail server's version is 4.5.3, it is pretty old.

Is there any update to this thread? I notice that I'll all the responses to this issue, the resolution is that the hostname file or DNS settings are incorrect or that there are expired certificates. This is not true in all cases. In mice0217's example, you can see him clearly killing the processes but having it fail again on starting services.

In my cases this is the exact same thing that happens. I have my services stop for backup, kill lingering processes, run backup, start up, fail. This only happens on occasion, which is strange. I even threw in my script to kill lingering processes again before the services start back up and it still fails on occasion. Right before starting I even do a 'ps aux' in my script, which shows that there is no ldap process. I've run the command to check my certs expiration date, no problem. This issue just recently started happening, even though I've made no changes to any configuration. The system has been up and running for a couple years now with no other issues.

I AM able to get the system up and running by manually killing the process and then starting the services. Again, it's only on occasion now that I kill the processes in my backup script.